The present invention relates generally to vehicular braking systems and more particularly to a flow control valve and pressure regulator for limiting the communication of pressurized fluid from a pump to a vehicle braking system having anti-skid or anti-lock features.
Automobile drivers accustomed to driving under snowy or icy conditions are familiar with the technique of "pumping" the brake pedal so as to cyclically increase and decrease the braking force exerted on the wheels in order that a slipping wheel having a tendency to lock is permitted to re-accelerate back to a speed corresponding to the speed of the vehicle. Such a driver induced anti-skid technique is simulated by many known devices into anti-lock braking systems.
Some anti-lock braking systems operate on a so-called pump-back principle where the same hydraulic fluid is resupplied to the brake pad actuators subsequent to an anti-skid event while others operate of a replenish principle where the reapply or build fluid comes from a separate source such as a hydraulic accumulator.
U.S. Pat. No. 4,218,100 discloses an anti-lock braking system having an anti-skid valve between an operator-controlled pressure source and a brake actuator. In this system, the fluid connection between the source and actuator is interrupted and fluid is directed from the actuator to a low pressure reservoir when a skid is detected. There is a second source of pressurized fluid and a pressure responsive valve which opens to replenish the fluid supply to the actuator when the pressure difference between the operator-controlled pressure source and the brake actuator exceeds a predetermined value. U.S. Pat. No. 4,750,788 discloses a modulation valve for use in a traction control system to selectively control the communication of pressurized fluid to effect a brake application during acceleration of a vehicle to synchronize the application of torque to drive wheels.
U.S. Pat. No. 5,354,123 filed Nov. 5, 1992, discloses a braking system having a flow control valve which interconnects a pressure source, a low pressure return, and a braking device for directing fluid from the source to the braking device when in a first state and for directing fluid from the braking device to the return when in a second state. A spring-loaded accumulator receives and stores pressurized hydraulic fluid, and a fixed size fluid passing aperture selectively provides a limited flow of hydraulic fluid from the accumulator to the hydraulically actuated wheel rotation braking device to rebuild the braking force after a skid has been detected and corrected for. Unfortunately, this system requires numerous check valves in addition to the accumulators.
In low-cost electrohydraulic braking systems, it is difficult to restrict the reapply rate after an antilock event since normal braking is done through the same valve members. U.S. Pat. No. 5,046,788 discloses a quick release valve for use in a brake system to switch from an anti lock function in a brake system to a normal braking application.
It is desirable to provide a simple, quiet replenishment type system having no accumulators and lacking the typical numerous check valves associated with prior devices where appropriate control of the reapply rate can be achieved.